drm/i915/display: Migrate objects to LMEM if possible for display

Objects intended to be used as display framebuffers must reside in
LMEM for discrete. If they happen to not do that, migrate them to
LMEM before pinning.

Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210629151203.209465-4-thomas.hellstrom@linux.intel.com